Benefits of a Comprehensive Infiltration and Inflow Removal Program

The sanitary sewer flow from the City of New Britain, Connecticut (City) is conveyed to the Mattabasset District in nearby Cromwell, Connecticut for treatment. The Mattabasset District has allotted the City 22.5 MGD for their sanitary flows. There are times the City exceeds its treatment allotment, so the City is targeting and reducing sources of infiltration and inflow (I/I) in their system. The City has 18,000 service connections, approximately 3,600 sanitary sewer manholes, and 180 miles of gravity sanitary sewer mains. Approximately 20% of the City's collection system is over 100 years old, with some dating back to the 1870s. Since 1998, the City spent vast resources and efforts into understanding its sewer system defects and identifying sources of I/I. The City performed a system-wide flow metering program beginning in 2011 and found I/I in several metersheds. The City has followed up with field work and completed multiple sewer rehabilitation projects in these metersheds. The City initially focused on removing I/I from public portions of the collection system. Flow metering results following this I/I removal showed a reduction in peak flow but subsequent meter results showed flows increase back up to pre-I/I removal conditions. This forced the City to implement comprehensive I/I removal to remain below their treatment allotment. The comprehensive removal, which includes targeted public and private rehabilitation, has shown significant reduction in I/I. This presentation will focus on lessons learned for various rehabilitation methods and provide insight into managing multiple years of flow and condition assessment data.